Organic electronic devices using phthalimide compounds

ABSTRACT

Organic electronic devices comprising a phthalimide compound. The phthalimide compounds disclosed herein are electron transporters with large HOMO-LUMO gaps, high triplet energies, large reduction potentials, and/or thermal and chemical stability. As such, these phthalimide compounds are suitable for use in any of various organic electronic devices, such as OLEDs and solar cells. In an OLED, the phthalimide compounds may serve various functions, such as a host in the emissive layer, as a hole blocking material, or as an electron transport material. In a solar cell, the phthalimide compounds may serve various functions, such as an exciton blocking material. Various examples of phthalimide compounds which may be suitable for use in the present invention are disclosed.

This application is a continuation of U.S. Ser. No. 12/854,297, filedAug. 11, 2010, which is a continuation of U.S. Ser. No. 11/783,817,filed on Apr. 12, 2007, which claims priority to U.S. ProvisionalApplication Ser. No. 60/792,120 filed on Apr. 13, 2006, both of whichare incorporated by reference in their entireties.

This invention was made with support from the United States Government,under Contract No. DE-FG02-03ER83813, awarded by the U.S. Dept. ofEnergy. The Government may have certain rights in this invention.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Princeton University, The University ofSouthern California, and the Universal Display Corporation. Theagreement was in effect on and before the date the claimed invention wasmade, and the claimed invention was made as a result of activitiesundertaken within the scope of the agreement.

TECHNICAL FIELD

The present invention relates to organic electronic devices.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A. dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules. In general, a small molecule has a well-definedchemical formula with a single molecular weight, whereas a polymer has achemical formula and a molecular weight that may vary from molecule tomolecule. As used herein, “organic” includes metal complexes ofhydrocarbyl and heteroatom-substituted hydrocarbyl ligands.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

OLED devices are generally (but not always) intended to emit lightthrough at least one of the electrodes, and one or more transparentelectrodes may be useful in an organic opto-electronic devices. Forexample, a transparent electrode material, such as indium tin oxide(ITO), may be used as the bottom electrode. A transparent top electrode,such as disclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745, which areincorporated by reference in their entireties, may also be used. For adevice intended to emit light only through the bottom electrode, the topelectrode does not need to be transparent, and may be comprised of athick and reflective metal layer having a high electrical conductivity.Similarly, for a device intended to emit light only through the topelectrode, the bottom electrode may be opaque and/or reflective. Wherean electrode does not need to be transparent, using a thicker layer mayprovide better conductivity, and using a reflective electrode mayincrease the amount of light emitted through the other electrode, byreflecting light back towards the transparent electrode. Fullytransparent devices may also be fabricated, where both electrodes aretransparent. Side emitting OLEDs may also be fabricated, and one or bothelectrodes may be opaque or reflective in such devices.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. For example, for a devicehaving two electrodes, the bottom electrode is the electrode closest tothe substrate, and is generally the first electrode fabricated. Thebottom electrode has two surfaces, a bottom surface closest to thesubstrate, and a top surface further away from the substrate. Where afirst layer is described as “disposed over” a second layer, the firstlayer is disposed further away from substrate. There may be other layersbetween the first and second layer, unless it is specified that thefirst layer is “in physical contact with” the second layer. For example,a cathode may be described as “disposed over” an anode, even thoughthere are various organic layers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

SUMMARY

In one aspect, the present invention provides an organic electronicdevice comprising: an anode; a cathode; and an organic layer disposedbetween the anode and the cathode, wherein the organic layer comprises aphthalimide compound having the formula:

wherein R₁ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution is ahydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety, and wherein R is a phenyl group or a phthalimide-containinggroup.

In another aspect, the present invention provides an organic electronicdevice comprising: an anode; a cathode; and an organic layer disposedbetween the anode and the cathode, wherein the organic layer comprises aphthalimide compound having the formula:

wherein R_(A) represents one or more independently selectedsubstitutions located on any position of the ring, wherein eachsubstitution is a hydrogen, an alkyl moiety containing up to fifteencarbon atoms, or an aryl moiety, wherein R_(B) represents one or moreindependently selected substitutions located on any position of thering, wherein each substitution is a hydrogen, an alkyl moietycontaining up to fifteen carbon atoms, or an aryl moiety, and wherein Lis a 6-membered ring or a direct bond between the two phthalimidegroups.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device having separate electrontransport, hole transport, and emissive layers, as well as other layers.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows a plot of quantum efficiency v. current density for devicesA1-A3.

FIG. 4 shows a plot of brightness v. voltage for devices A1-A3.

FIG. 5 shows a plot current density v. voltage for device A1-A3.

FIG. 6 shows the electroluminescent spectra for devices A1-A3.

FIG. 7 shows a plot of quantum efficiency v. current density for devicesB1-B4.

FIG. 8 shows a plot of brightness v. voltage for devices B1-B4.

FIG. 9 shows a plot of current density v. voltage for devices B1-B4.

FIG. 10 shows the electroluminescent spectra for devices B1-B4.

FIG. 11 shows a plot of quantum efficiency v. current density fordevices C1-C4.

FIG. 12 shows the electroluminescent spectra for devices C1-C4.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 1, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence may be referred to asa “forbidden” transition because the transition requires a change inspin states, and quantum mechanics indicates that such a transition isnot favored. As a result, phosphorescence generally occurs in a timeframe exceeding at least 10 nanoseconds, and typically greater than 100nanoseconds. If the natural radiative lifetime of phosphorescence is toolong, triplets may decay by a non-radiative mechanism, such that nolight is emitted. Organic phosphorescence is also often observed inmolecules containing heteroatoms with unshared pairs of electrons atvery low temperatures. 2,2′-bipyridine is such a molecule. Non-radiativedecay mechanisms are typically temperature dependent, such that anorganic material that exhibits phosphorescence at liquid nitrogentemperatures typically does not exhibit phosphorescence at roomtemperature. But, as demonstrated by Baldo, this problem may beaddressed by selecting phosphorescent compounds that do phosphoresce atroom temperature. Representative emissive layers include doped orun-doped phosphorescent organometallic materials such as disclosed inU.S. Pat. Nos. 6,303,238 and 6,310,360; U.S. Patent ApplicationPublication Nos. 2002-0034656; 2002-0182441; 2003-0072964; andWO-02/074015.

Generally, the excitons in an OLED are believed to be created in a ratioof about 3:1, i.e., approximately 75% triplets and 25% singlets. See,Adachi et al., “Nearly 100% Internal Phosphorescent Efficiency In AnOrganic Light Emitting Device,” J. Appl. Phys., 90, 5048 (2001), whichis incorporated by reference in its entirety. In many cases, singletexcitons may readily transfer their energy to triplet excited states via“intersystem crossing,” whereas triplet excitons may not readilytransfer their energy to singlet excited states. As a result, 100%internal quantum efficiency is theoretically possible withphosphorescent OLEDs. In a fluorescent device, the energy of tripletexcitons is generally lost to radiationless decay processes that heat-upthe device, resulting in much lower internal quantum efficiencies. OLEDsutilizing phosphorescent materials that emit from triplet excited statesare disclosed, for example, in U.S. Pat. No. 6,303,238, which isincorporated by reference in its entirety.

Phosphorescence may be preceded by a transition from a triplet excitedstate to an intermediate non-triplet state from which the emissive decayoccurs. For example, organic molecules coordinated to lanthanideelements often phosphoresce from excited states localized on thelanthanide metal. However, such materials do not phosphoresce directlyfrom a triplet excited state but instead emit from an atomic excitedstate centered on the lanthanide metal ion. The europium diketonatecomplexes illustrate one group of these types of species.

Phosphorescence from triplets can be enhanced over fluorescence byconfining, preferably through bonding, the organic molecule in closeproximity to an atom of high atomic number. This phenomenon, called theheavy atom effect, is created by a mechanism known as spin-orbitcoupling. Such a phosphorescent transition may be observed from anexcited metal-to-ligand charge transfer (MLCT) state of anorganometallic molecule such as tris(2-phenylpyridine)iridium(III).

As used herein, the term “triplet energy” refers to an energycorresponding to the highest energy feature discernable in thephosphorescence spectrum of a given material. The highest energy featureis not necessarily the peak having the greatest intensity in thephosphorescence spectrum, and could, for example, be a local maximum ofa clear shoulder on the high energy side of such a peak.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order.

Substrate 110 may be any suitable substrate that provides desiredstructural properties. Substrate 110 may be flexible or rigid. Substrate110 may be transparent, translucent or opaque. Plastic and glass areexamples of preferred rigid substrate materials. Plastic and metal foilsare examples of preferred flexible substrate materials. Substrate 110may be a semiconductor material in order to facilitate the fabricationof circuitry. For example, substrate 110 may be a silicon wafer uponwhich circuits are fabricated, capable of controlling OLEDs subsequentlydeposited on the substrate. Other substrates may be used. The materialand thickness of substrate 110 may be chosen to obtain desiredstructural and optical properties.

Anode 115 may be any suitable anode that is sufficiently conductive totransport holes to the organic layers. The material of anode 115preferably has a work function higher than about 4 eV (a “high workfunction material”). Preferred anode materials include conductive metaloxides, such as indium tin oxide (ITO) and indium zinc oxide (IZO),aluminum zinc oxide (AlZnO), and metals. Anode 115 (and substrate 110)may be sufficiently transparent to create a bottom-emitting device. Apreferred transparent substrate and anode combination is commerciallyavailable ITO (anode) deposited on glass or plastic (substrate). Aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. Nos. 5,844,363 and 6,602,540 B2, which are incorporated byreference in their entireties. Anode 115 may be opaque and/orreflective. A reflective anode 115 may be preferred for sometop-emitting devices, to increase the amount of light emitted from thetop of the device. The material and thickness of anode 115 may be chosento obtain desired conductive and optical properties. Where anode 115 istransparent, there may be a range of thickness for a particular materialthat is thick enough to provide the desired conductivity, yet thinenough to provide the desired degree of transparency. Other anodematerials and structures may be used.

Hole transport layer 125 may include a material capable of transportingholes. Hole transport layer 130 may be intrinsic (undoped), or doped.Doping may be used to enhance conductivity. α-NPD and TPD are examplesof intrinsic hole transport layers. An example of a p-doped holetransport layer is m-MTDATA doped with F₄-TCNQ at a molar ratio of 50:1,as disclosed in United States Patent Application Publication No.2003-0230980 to Forrest et al., which is incorporated by reference inits entirety. Other hole transport layers may be used.

Emissive layer 135 may include an organic material capable of emittinglight when a current is passed between anode 115 and cathode 160.Preferably, emissive layer 135 contains a phosphorescent emissivematerial, although fluorescent emissive materials may also be used.Phosphorescent materials are preferred because of the higher luminescentefficiencies associated with such materials. Emissive layer 135 may alsocomprise a host material capable of transporting electrons and/or holes,doped with an emissive material that may trap electrons, holes, and/orexcitons, such that excitons relax from the emissive material via aphotoemissive mechanism. Emissive layer 135 may comprise a singlematerial that combines transport and emissive properties. Whether theemissive material is a dopant or a major constituent, emissive layer 135may comprise other materials, such as dopants that tune the emission ofthe emissive material. Emissive layer 135 may include a plurality ofemissive materials capable of, in combination, emitting a desiredspectrum of light. Examples of phosphorescent emissive materials includeIr(ppy)₃. Examples of fluorescent emissive materials include DCM andDMQA. Examples of host materials include Alq₃, CBP and mCP. Examples ofemissive and host materials are disclosed in U.S. Pat. No. 6,303,238 toThompson et al., which is incorporated by reference in its entirety.Emissive material may be included in emissive layer 135 in a number ofways. For example, an emissive small molecule may be incorporated into apolymer. This may be accomplished by several ways: by doping the smallmolecule into the polymer either as a separate and distinct molecularspecies; or by incorporating the small molecule into the backbone of thepolymer, so as to form a co-polymer; or by bonding the small molecule asa pendant group on the polymer. Other emissive layer materials andstructures may be used. For example, a small molecule emissive materialmay be present as the core of a dendrimer.

Many useful emissive materials include one or more ligands bound to ametal center. A ligand may be referred to as “photoactive” if itcontributes directly to the photoactive properties of an organometallicemissive material. A “photoactive” ligand may provide, in conjunctionwith a metal, the energy levels from which and to which an electronmoves when a photon is emitted. Other ligands may be referred to as“ancillary.” Ancillary ligands may modify the photoactive properties ofthe molecule, for example by shifting the energy levels of a photoactiveligand, but ancillary ligands do not directly provide the energy levelsinvolved in light emission. A ligand that is photoactive in one moleculemay be ancillary in another. These definitions of photoactive andancillary are intended as non-limiting theories.

Electron transport layer 145 may include a material capable oftransporting electrons. Electron transport layer 145 may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity. Alq₃ isan example of an intrinsic electron transport layer. An example of ann-doped electron transport layer is BPhen doped with Li at a molar ratioof 1:1, as disclosed in United States Patent Application Publication No.2003-0230980 to Forrest et al., which is incorporated by reference inits entirety. Other electron transport layers may be used.

The charge carrying component of the electron transport layer may beselected such that electrons can be efficiently injected from thecathode into the LUMO (Lowest Unoccupied Molecular Orbital) energy levelof the electron transport layer. The “charge carrying component” is thematerial responsible for the LUMO energy level that actually transportselectrons. This component may be the base material, or it may be adopant. The LUMO energy level of an organic material may be generallycharacterized by the electron affinity of that material and the relativeelectron injection efficiency of a cathode may be generallycharacterized in terms of the work function of the cathode material.This means that the preferred properties of an electron transport layerand the adjacent cathode may be specified in terms of the electronaffinity of the charge carrying component of the ETL and the workfunction of the cathode material. In particular, so as to achieve highelectron injection efficiency, the work function of the cathode materialis preferably not greater than the electron affinity of the chargecarrying component of the electron transport layer by more than about0.75 eV, more preferably, by not more than about 0.5 eV. Similarconsiderations apply to any layer into which electrons are beinginjected.

Cathode 160 may be any suitable material or combination of materialsknown to the art, such that cathode 160 is capable of conductingelectrons and injecting them into the organic layers of device 100.Cathode 160 may be transparent or opaque, and may be reflective. Metalsand metal oxides are examples of suitable cathode materials. Cathode 160may be a single layer, or may have a compound structure. FIG. 1 shows acompound cathode 160 having a thin metal layer 162 and a thickerconductive metal oxide layer 164. In a compound cathode, preferredmaterials for the thicker layer 164 include ITO, IZO, and othermaterials known to the art. U.S. Pat. Nos. 5,703,436, 5,707,745,6,548,956 B2 and 6,576,134 B2, which are incorporated by reference intheir entireties, disclose examples of cathodes including compoundcathodes having a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thepart of cathode 160 that is in contact with the underlying organiclayer, whether it is a single layer cathode 160, the thin metal layer162 of a compound cathode, or some other part, is preferably made of amaterial having a work function lower than about 4 eV (a “low workfunction material”). Other cathode materials and structures may be used.

Blocking layers may be used to reduce the number of charge carriers(electrons or holes) and/or excitons that leave the emissive layer. Anelectron blocking layer 130 may be disposed between emissive layer 135and the hole transport layer 125, to block electrons from leavingemissive layer 135 in the direction of hole transport layer 125.Similarly, a hole blocking layer 140 may be disposed between emissivelayer 135 and electron transport layer 145, to block holes from leavingemissive layer 135 in the direction of electron transport layer 145.Blocking layers may also be used to block excitons from diffusing out ofthe emissive layer. The theory and use of blocking layers is describedin more detail in U.S. Pat. No. 6,097,147 and United States PatentApplication Publication No. 2003-0230980 to Forrest et al., which areincorporated by reference in their entireties.

As used herein, and as would be understood by one skilled in the art,the term “blocking layer” means that the layer provides a barrier thatsignificantly inhibits transport of charge carriers and/or excitonsthrough the device, without suggesting that the layer necessarilycompletely blocks the charge carriers and/or excitons. The presence ofsuch a blocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

Generally, injection layers are comprised of a material that may improvethe injection of charge carriers from one layer, such as an electrode oran organic layer, into an adjacent organic layer. Injection layers mayalso perform a charge transport function. In device 100, hole injectionlayer 120 may be any layer that improves the injection of holes fromanode 115 into hole transport layer 125. CuPc is an example of amaterial that may be used as a hole injection layer from an ITO anode115, and other anodes. In device 100, electron injection layer 150 maybe any layer that improves the injection of electrons into electrontransport layer 145. LiF/Al is an example of a material that may be usedas an electron injection layer into an electron transport layer from anadjacent layer. Other materials or combinations of materials may be usedfor injection layers. Depending upon the configuration of a particulardevice, injection layers may be disposed at locations different thanthose shown in device 100. More examples of injection layers areprovided in U.S. patent application Ser. No. 09/931,948 to Lu et al.,which is incorporated by reference in its entirety. A hole injectionlayer may comprise a solution deposited material, such as a spin-coatedpolymer, e.g., PEDOT:PSS, or it may be a vapor deposited small moleculematerial, e.g., CuPc or MTDATA.

A hole injection layer (HIL) may planarize or wet the anode surface soas to provide efficient hole injection from the anode into the holeinjecting material. A hole injection layer may also have a chargecarrying component having HOMO (Highest Occupied Molecular Orbital)energy levels that favorably match up, as defined by theirherein-described relative ionization potential (IP) energies, with theadjacent anode layer on one side of the HIL and the hole transportinglayer on the opposite side of the HIL. The “charge carrying component”is the material responsible for the HOMO energy level that actuallytransports holes. This component may be the base material of the HIL, orit may be a dopant. Using a doped HIL allows the dopant to be selectedfor its electrical properties, and the host to be selected formorphological properties such as wetting, flexibility, toughness, etc.Preferred properties for the HIL material are such that holes can beefficiently injected from the anode into the HIL material. Inparticular, the charge carrying component of the HIL preferably has anIP not more than about 0.7 eV greater that the IP of the anode material.More preferably, the charge carrying component has an IP not more thanabout 0.5 eV greater than the anode material. Similar considerationsapply to any layer into which holes are being injected. HIL materialsare further distinguished from conventional hole transporting materialsthat are typically used in the hole transporting layer of an OLED inthat such HIL materials may have a hole conductivity that issubstantially less than the hole conductivity of conventional holetransporting materials. The thickness of the HIL of the presentinvention may be thick enough to help planarize or wet the surface ofthe anode layer. For example, an HIL thickness of as little as 10 nm maybe acceptable for a very smooth anode surface. However, since anodesurfaces tend to be very rough, a thickness for the HIL of up to 50 nmmay be desired in some cases.

A protective layer may be used to protect underlying layers duringsubsequent fabrication processes. For example, the processes used tofabricate metal or metal oxide top electrodes may damage organic layers,and a protective layer may be used to reduce or eliminate such damage.In device 100, protective layer 155 may reduce damage to underlyingorganic layers during the fabrication of cathode 160. Preferably, aprotective layer has a high carrier mobility for the type of carrierthat it transports (electrons in device 100), such that it does notsignificantly increase the operating voltage of device 100. CuPc, BCP,and various metal phthalocyanines are examples of materials that may beused in protective layers. Other materials or combinations of materialsmay be used. The thickness of protective layer 155 is preferably thickenough that there is little or no damage to underlying layers due tofabrication processes that occur after organic protective layer 160 isdeposited, yet not so thick as to significantly increase the operatingvoltage of device 100. Protective layer 155 may be doped to increase itsconductivity. For example, a CuPc or BCP protective layer 160 may bedoped with Li. A more detailed description of protective layers may befound in U.S. patent application Ser. No. 09/931,948 to Lu et al., whichis incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,an cathode 215, an emissive layer 220, a hole transport layer 225, andan anode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190, Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink-jet and OVJP.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, may be used in small molecules to enhance their ability toundergo solution processing. Materials with asymmetric structures mayhave better solution processibility than those having symmetricstructures, because asymmetric materials may have a lower tendency torecrystallize. Dendrimer substituents may be used to enhance the abilityof small molecules to undergo solution processing.

The molecules disclosed herein may be substituted in a number ofdifferent ways without departing from the scope of the invention. Forexample, substituents may be added to a compound having three bidentateligands, such that after the substituents are added, one or more of thebidentate ligands are linked together to form, for example, atetradentate or hexadentate ligand. Other such linkages may be formed.It is believed that this type of linking may increase stability relativeto a similar compound without linking, due to what is generallyunderstood in the art as a “chelating effect.”

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

In one aspect, the present invention provides organic electronic devicesusing phthalimide compounds having the formula:

wherein R₁ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution is ahydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety, and wherein R is a phenyl group or a phthalimide-containinggroup.

The term “aryl moiety,” as used herein, refers to structures containingat least one aromatic ring, including single-ring groups as well aspolycyclic ring systems. The polycyclic rings may have two or more ringsin which two atoms are common by two adjoining rings (i.e., the ringsare “fused”) wherein at least one of the rings is aromatic. Arylmoieties suitable for use as substituents in the present inventioninclude phenyl, and oligoaryls such as naphthyl, biphenyl, andphenanthryl.

In some instances, R is a phthalimide-containing group represented bythe formula:

wherein R₂ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution ishydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety, wherein R₈ represents a substitution located on anyposition of the ring, wherein R₈ is phthalimide represented by theformula:

and wherein R₃ represents one or more independently selectedsubstitutions located on any position of the ring, wherein eachsubstitution is a hydrogen, an alkyl moiety containing up to fifteencarbon atoms, or an aryl moiety. The two phthalimide groups may be inortho, meta, or para position on the central phenyl ring.

In some cases, the two phthalimide groups are in para position on thecentral phenyl ring. In some cases, each R₃ is selected from the groupconsisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, tert-butyl, phenyl, naphthyl, biphenyl, and phenanthryl. Insome cases, each R₂ is selected from the group consisting of hydrogen,methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, phenyl,naphthyl, biphenyl, and phenanthryl. In some cases, each R₁ is selectedfrom the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl,butyl, isobutyl, tert-butyl, phenyl, naphthyl, biphenyl, andphenanthryl.

In some instances, R is a phthalimide-containing group represented bythe formula:

wherein R₄ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution ishydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety, and wherein R₅ represents a substitution located on anyposition of the ring, wherein R₅ is represented by the formula:

wherein R₆ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution ishydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety. The two phthalimide groups may be in ortho, meta, or paraposition on the cyclohexane ring.

In some cases, the two phthalimide groups are in ortho position on thecyclohexane ring. In some cases, each R₄ is independently selected fromthe group consisting of hydrogen, methyl, ethyl, propyl, isopropyl,butyl, isobutyl, tert-butyl, phenyl, naphthyl, biphenyl, andphenanthryl. In some cases, each R₆ is independently selected from thegroup consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, tert-butyl, phenyl, naphthyl, biphenyl, and phenanthryl.

In some instances, R is a phenyl ring, with or without alkyl moietysubstitutions containing up to fifteen carbon atoms, or aryl moietysubstitutions. In some cases, the substitutions may be selected from thegroup consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, tert-butyl, phenyl, naphthyl, biphenyl, and phenanthryl. Insome cases, the phenyl ring has no substitutions.

Examples of phthalimide compounds suitable for use in the presentinvention include the following:

In another aspect, the present invention provides organic electronicdevices using phthalimide compounds having the formula:

wherein R_(A) represents one or more independently selectedsubstitutions located on any position of the ring, wherein eachsubstitution is a hydrogen, an alkyl moiety containing up to fifteencarbon atoms, or an aryl moiety, wherein R_(B) represents one or moreindependently selected substitutions located on any position of thering, wherein each substitution is a hydrogen, an alkyl moietycontaining up to fifteen carbon atoms, or an aryl moiety, and wherein Lis a 6-membered ring or a direct bond between the two phthalimidegroups.

In some instances, L is a cyclohexane ring represented by the formula:

wherein R_(C) represents one or more independently selectedsubstitutions located on any position of the ring, wherein eachsubstitution is a hydrogen, an alkyl moiety containing up to fifteencarbon atoms, or an aryl moiety, and wherein the two phthalimide groupsare in ortho, meta, or para position on the cyclohexane ring.

In some cases, the two phthalimide groups on the cyclohexane ring are inortho position. In some cases, each of R_(C) on the cyclohexane ishydrogen. In some cases, each R_(A) is independently selected from thegroup consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, tert-butyl, phenyl, naphthyl, biphenyl, and phenanthryl. Insome cases, each R_(B) is independently selected from the groupconsisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, tert-butyl, phenyl, naphthyl, biphenyl, and phenanthryl. Insome cases, each R_(A) is a tert-butyl and each R_(B) is a tert-butyl.

In some instances, L is a phenyl ring represented by the formula:

wherein R_(D) represents one or more independently selectedsubstitutions located on any position of the ring, wherein eachsubstitution is a hydrogen, an alkyl moiety containing up to fifteencarbon atoms, or an aryl moiety, and wherein the two phthalimide groupsare in ortho, meta, or para position on the phenyl ring.

In some cases, the two phthalimide groups on the phenyl ring are in paraposition. In some cases, each of R_(D) on the cyclohexane is hydrogen.In some cases, each of R_(D) on the cyclohexane is methyl. In somecases, each R_(A) is independently selected from the group consisting ofhydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl,phenyl, naphthyl, biphenyl, and phenanthryl. In some cases, each R_(B)is independently selected from the group consisting of hydrogen, methyl,ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, phenyl, naphthyl,biphenyl, and phenanthryl. In some cases, each R_(A) is a tert-butyl andeach R_(B) is a tert-butyl.

The phthalimide compounds disclosed herein are electron transporterswith large HOMO-LUMO gaps, high triplet energies, large reductionpotentials, and/or thermal and chemical stability. As such, thesephthalimide compounds are suitable for use in any of various organicelectronic devices, such as OLEDs and solar cells. In OLEDs, thephthalimide compounds may be used in any of the various layers of theOLED. For example, the phthalimide compounds may be used in the emissivelayer (as a host material, for instance). In another example, thephthalimide compounds may be used in the hole blocking layer (as a holeblocking material, for instance). In another example, the phthalimidecompounds may be used in an electron blocking layer. The phthalimidecompounds may also be used in solar cells. For example, the compoundsmay be used in the exciton blocking layer of a solar cell.

Compound Synthesis Examples

As shown in the reactions schemes below, synthesis of the targetcompounds (6-9) was performed in one step from commercially availablephthalic anhydride 1; 4-tert-butyl phthalic anhydride 2;phenyl-1,2-diamine 3; 2,3,5,6-tetramethyl-phenyl-1,2-diamine 4; andcyclohexane-1,4-diamine 5. All reactions were conducted inside amicrowave reactor in a solvent free environment. Phthalimide compounds 6and 7 were synthesized by irradiating the mixtures of anhydride 1 witheither amine 3 or amine 4 in two different reactions. The tert-butylphthalimide compounds 8 and 9 were made in a similar fashion by reactingthe tert-butyl anhydride 2 with either amine 4 or amine 5 undermicrowave conditions separately.

General Procedure. The reactant anhydrides and the amines were mixed intwo different ways before synthesis. These reactants were either drymixed and ground to fine powders in a mortar and pestle or mixed withdichloromethane, stirred for ten minutes, and then concentrated invacuo.

Phenyl-1,4-bis-phthalimide (Compound P-2p). A mixture ofphenyl-1,2-diamine 3 (1 equiv) and phthalic anhydride 1 (3 equiv) wassubjected to microwave (300 W) irradiation at 250° C. for 40 minutes.The dark colored insoluble material was then sublimed at 265° C. to giveoff-white crystals of phthalimide compound P-2p in 80% yield. AnalysisData: ¹H NMR (250 MHz, CDCl₃): δ 8.01 (dd, 4H), δ 7.80 (dd, 4H).Elemental analysis results: C=71.55; H=3.20; N=7.61, compared tocalculated values of C=71.74; H=3.28; N=7.61 for C₂₂H₁₂N₂O₄.

2,3,5,6-tetramethyl-phenyl-1,4-(bis-phthalimide) (Compound TMPP). Asolid solution of 2,3,5,6-tetramethyl-phenyl-1,2-diamine 4 (1 equiv) andphthalic anhydride 1 (3 equiv) was placed inside the 300 W microwavereactor and heated to 250° C. for 40 minutes. The dark brown materialwas sublimed at 285° C. to afford light yellow crystals of phthalimidecompound TMPP in 80% yield. Analysis Data: Mp (DSC) 462° C. ¹H NMR (250MHz, CDCl₃): δ 8.01 (dd, 4H), δ 7.80 (dd, 4H), δ 1.57 (s, 12H).Elemental analysis results: C=73.70; H=4.66; N=6.60, compared tocalculated values of C=73.57; H=4.75; N=6.60 for C₂₆H₂₀N₂O₄.

2,3,5,6-tetramethyl-phenyl-1,4-bis-(4-tert-butylphthalimide) (CompoundTMPP*). A mixture of 2,3,5,6-tetramethyl-phenyl-1,2-diamine 4 (1 equiv)and 4-t-butyl phthalic anhydride 2 (3 equiv) was placed inside themicrowave reactor (300 W) and irradiated for 40 minutes at 120° C. Theyellow colored crude was passed through a short column of silica gel indichloromethane. Concentration of this elute followed by a flashchromatographic purification of the crude (SiO₂, dichloromethane) gavephthalimide compound TMPP* as white powder in 85% yield. Analysis Data:Mp (DSC) 413° C., T_(g) (DSC) 88° C., T_(c) (DSC) 189° C. ¹H NMR (360MHz, CDCl₃): δ 8.01 (d, J=0.003 Hz, 2H), δ 7.90 (dd, J=0.043 Hz, 4H), δ2.09 (s, 12H), δ 1.43 (s, 18H). Elemental analysis results: C=76.31;H=6.75; N=5.31, compared to calculated values of C=76.09; H=6.76; N=5.22for C₃₄H₃₆N₂O₄.

1,2-bis-(4-tert-butylphthalimide)-cyclohexane (Compound CH-2p).Cyclohexane-1,4-diamine 5 (1 equiv) was mixed with 4-tert-butyl phthalicanhydride 2 (3 equiv) in dichloromethane (20 ml). The reaction mixturewas then stirred for 10 minutes, concentrated in vacuo, and subjected tomicrowave (300 W) reaction for 30 minutes at 250° C. The dark yellowcrude was then passed through a silica gel filter, concentrated, andsubjected to flash chromatography (silica gel) in dichloromethane togive pure yellow crystals of phthalimide compound CH-2p in 60% yield.Analysis Data: Mp (DSC) 388° C., T_(g) (DSC) 88° C. ¹H NMR (360 MHz,CDCl₃): δ 7.70 (br m, 6H), δ 5.07 (m, J=0.008 Hz, 2H), δ 2.37 (br m,2H), δ 1.88 (br m, 4H), δ 1.57 (br m, 2H), δ 1.31 (s, 18H). Elementalanalysis results: C=74.11; H=6.99; N=5.78, compared with calculatedvalues of C=74.05; H=7.04; N=5.76 for C₃₀ H₃₄N₂O₄.

Solution photophysics data of various of the phthalimide compounds areshown in Table 1 below. These data indicate that the phthalimidecompounds have high triplet energies and lifetimes in the millisecondrange.

TABLE 1 λ_(max)(298K) E_(s) τ_(S) λ_(max)(77K) E_(T) τ_(T) Compound (nm)Φ_(S) (nm/eV) (ns) (nm) (nm/eV) (ms) NPP — — 313/196 — 410, 420, 442410/3.02 667 TMPP — —  313/3.96 — 426, 448 426/2.91 360 TMPP* 447 — 318/3.90 — 316, 445, 380, 456 430/2.9  450 P-2p — — 313/196 — 355, 432,448 432/2.87 349 P-1p 495 — 322/185 — 360, 449 449/2.76 224 CH-2p 4005.2E−05  318/3.90 <5 381, 452 452/2.74 590

Device Examples

Phthalimide compounds TMPP and TMPP* were used in fabricating OLEDs. AllOLEDs were fabricated on ITO-coated glass substrates and circuitpatterns were photolithographically imprinted on the substrates as 2 mmwide stripes with 1 mm spacings. Surface resistivity of the ITO coatingwas measured to be approximately 20Ω⁻¹. The ITO coated substrates werethen rinsed with acetone, sonicated in soap-water solution, and boiledin trichloroethylene, acetone, and ethanol for 5 minutes each.Afterwards, the substrates were treated for ten minutes in the UV-ozonecleaning chamber.

The OLEDs were fabricated inside a high vacuum chamber (Kurt J. Lesker)equipped with a cryo pump, two crystal monitors, and two power sources.Organic films were thermally evaporated onto the ITO substrates fromtantalum boats at pressures between 3-4 μtorr. Deposition rates for allthe organic materials were maintained to be between 2-4 Å/s at alltimes. Prior to the deposition of the cathode, the chamber was ventedwith nitrogen and shadow masks consisting of 2 mm stripes were placedonto the substrates. Once the pressure reached 3.0 μtorr, 10 Å oflithium fluoride (LiF) was deposited at 0.2 Å/s rate followed by a 1200Å layer of aluminum at rates between 4-5 Å/s.

Three sets of devices (A, B, and C) were fabricated on the ITOsubstrates having the general architecture: a 400 Å layer of NPD as thehole transport layer; a 250 Å layer of host:dopant as the emissivelayer; a 150 Å layer of a hole blocking material as the hole blockinglayer; a 150 Å layer of Alq₃ as the electron transport layer; and LiF(10 Å)/Al (1200 Å) as the cathode.

In device set A, fac-tris(2-phenylpyridinato-N,C²) iridium(III) (Irppy)was used as the dopant in the emissive layer. In Device A1 (control),CBP was used as the host in the emissive layer, and BCP was used as thehole blocking material. In Device A2, CBP was used as the host in theemissive layer, and TMPP* was used as the hole blocking material. InDevice A3, TMPP* was used as the host in the emissive layer, and BCP wasused as the hole blocking layer.

In device set B, bis(2-phenylquinolyl-N,C²) iridium(III) (PQIr) was usedas the dopant in the emissive layer. In Device B1 (control), CBP wasused as the host in the emissive layer, and BCP was used as the holeblocking material. In Device B2, CBP was used as the host in theemissive layer, and TMPP* was used as the hole blocking material. InDevice B3, TMPP* was used as the host in the emissive layer, and BCP wasused as the hole blocking material. In Device B4, TMPP* was used as boththe host in the emissive material and as the hole blocking material.

In device set C, PQIr was used as the dopant in the emissive layer.Device C1 (control) is the same as device B1. In Device C2, CBP was usedas the host in the emissive layer, and TMPP was used as the holeblocking material. In Device C3, TMPP was used as the host in theemissive layer, and BCP was used as the hole blocking material. InDevice C4, TMPP was used as both the host in the emissive material andas the hole blocking material.

All OLEDs were tested in room temperature and pressure in an openatmosphere. LabVIEW program was used to measure the brightness andcurrent-voltage (I-V) characteristics of the devices. A Keithley 2400source meter was used to power-up the OLEDs and light emitted from thefront of the devices were collected through a UV-818 Si photocathodeequipped with a Newport 1835-C optical meter. Electroluminescencespectra of the devices were recorded using a spectrofluorometer, modelC-60SE.

FIG. 3 shows a plot of quantum efficiency v. current density of devicesA1-A3. Device A3 (triangles), which uses TMPP* as the host and Irppy asthe dopant in the emissive layer, has low quantum efficiency because ofelectron transfer quenching of the host by the dopant. Device A2(half-filled circles), which uses TMPP* in the hole blocking layer, hashigh efficiency because of the hole/exciton blocking ability of TMPP*.In this case, Device A2 has more than twice the efficiency of controlDevice A1 (squares).

FIG. 4 shows a plot of brightness v. voltage of devices A1-A3. Device A3is dim because quenching of the TMPP* host by the Irppy dopant increasesthe non-radiative relaxation of the excited dopants. Device A2 is brightbecause the hole/exciton blocking by TMPP* increases the balancedrecombination and decreases the non-radiative relaxation of theexcitons. In this case, Device A2 is dimmer than control Device A1, butboth have approximately the same turn-on voltages.

FIG. 5 shows a plot current density v. voltage of devices A1-A3. DeviceA3 has current leakage and a high turn-on voltage. Electron transferfrom the excited dopant to the TMPP* host creates excess holes. BecauseI-V is dominated by electron flow, the electrons have low mobility, andexcess holes have to wait longer to recombine with electrons. Also,excess holes in the space charge limited (SCLC) region may create abarrier for incoming electrons by slightly changing the internalelectric field. These factors could prolong the turn-on voltage of thedevice. In comparison, Device A2 shows minimal shorts or currentleakage. In this case, the I-V shape and turn-on voltage of Device A2 iscomparable to control Device A1.

FIG. 6 shows the electroluminescent spectra of devices A1-A3. Device A3exhibits a λ_(max)=515 nm attributable to Irppy, with anotherλ_(max)=541, possibly attributable to emission from exciplexes formedbetween the TMPP* and NPD. Device A2 exhibits a λ_(max)=512 nmattributable to Irppy. Electroluminescence is only observed from thedopant. This data demonstrates that TMPP* performs well as an electrontransporter and a hole blocker.

FIG. 7 shows a plot of quantum efficiency v. current density of devicesB1-B4. Device B3 (inverted triangles), which uses TMPP* as the host andPQIr as the dopant in the emissive layer, has low quantum efficiencybecause of electron transfer quenching of the host by the dopant. DeviceB4 (upright triangles), which uses TMPP* as a host in the emissivematerial and as the hole blocking material, has very low quantumefficiency and a very short lifetime. In comparison to control Device B1(squares), Device B2 (circles) is very efficient because of thehole/exciton blocking capability of TMPP*. In this case, Device B2 ismore than 1.5 times efficient as control Device B1.

FIG. 8 shows a plot of brightness v. voltage of devices B1-B4. Device B3is dim because quenching of the TMPP* host by the Irppy dopant increasesthe non-radiative relaxation of the excited dopants. Likewise, Device B4is dim because of the quenching effect. Exciplexes (emissive ornon-emissive) formed between the TMPP* and NPD may also serve todecrease efficiency. Device B2 is bright and efficient because of thehole/exciton blocking ability of TMPP*, which increases the balancedrecombination and decreases the non-radiative relaxation of theexcitons. Because the triplet energy of TMPP* is much higher than thetriplet energy of PQIr, energy transfer is more efficient and the deviceis brighter. In this case, Device B2 is brighter than control Device B1.

FIG. 9 shows a plot of current density v. voltage of device B1-B4. TheI-V shape and turn-on voltage of Device B2 is similar to control DeviceB1. The I-V plot of Device 4 shows a shortage, but the I-V plot ofDevice 3 appears good. FIG. 10 shows the electroluminescent spectra ofdevices B1-B3. Each of these devices exhibit PQIr emission only.

FIG. 11 shows a plot of quantum efficiency v. current density of devicesC1-C4. Device C3 (inverted triangles), which uses TMPP as the host andPQIr as the dopant in the emissive layer, has low quantum efficiencybecause of electron transfer quenching of the host by the dopant. DeviceB4 (upright triangles), which uses TMPP as a host in the emissivematerial and as the hole blocking material, also has low quantumefficiency because of electron transfer quenching of the host by thedopant. Also, because TMPP has no glass transition temperature T_(g),crystalline islands may form upon deposition, which reduces energytransfer from TMPP to PQIr, allowing emission from Alq₃ to becomedominant.

FIG. 12 shows the electroluminescent spectra of devices C1-C4. DeviceC1-C3 exhibit PQIr emission only (λ_(max)=595 nm). Device C4 exhibitsAlq₃ emission (λ_(max)=510 nm) in addition to PQIr emission.

The above results demonstrate that using the phthalimide compoundsdisclosed herein in organic light-emitting devices can improve theperformance and efficiency of the devices.

MATERIAL DEFINITIONS

As used herein, abbreviations refer to materials as follows:

CBP: 4,4′-N,N′-dicarbazole-biphenyl

m-MTDATA 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine

Alq₃: 8-tris-hydroxyquinoline aluminum

BPhen: 4,7-diphenyl-1,10-phenanthroline

n-BPhen: n-doped BPhen (doped with lithium)

F₄-TCNQ: tetrafluoro-tetracyano-quinodimethane

p-MTDATA: p-doped m-MTDATA (doped with F₄-TCNQ)

Ir(ppy)₃: tris(2-phenylpyridine)-iridium

Ir(ppz)₃: tris(1-phenylpyrazoloto,N,C(2′)iridium(III)

BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline

TAZ: 3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole

CuPc: copper phthalocyanine.

ITO: indium tin oxide

NPD: N,N′-diphenyl-N—N′-di(1-naphthyl)-benzidine

TPD: N,N′-diphenyl-N—N′-di(3-toly)-benzidine

BAlq: aluminum(III)bis(2-methyl-8-hydroxyquinolinato)-4-phenylphenolate

mCP: 1,3-N,N-dicarbazole-benzene

DCM: 4-(dicyanoethylene)-6-(4-dimethylaminostyryl-2-methyl)-4H-pyran

DMQA: N,N′-dimethylquinacridone

1. An organic electronic device comprising: an anode; a cathode; and anorganic layer disposed between the anode and the cathode, wherein theorganic layer is capable of transporting electrons and comprises aphthalimide compound having the formula:

wherein R₁ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution is ahydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety, and wherein R is a phenyl group or a phthalimide-containinggroup.
 2. The device of claim 1, wherein R is represented by theformula:

wherein R₂ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution ishydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety, wherein R₈ represents a substitution located on anyposition of the ring, wherein R₈ is represented by the formula:

wherein R₃ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution is ahydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety.
 3. The device of claim 2, wherein the two phthalimidegroups are in para position on the phenyl ring.
 4. The device of claim1, wherein R is represented by the formula:

wherein R₄ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution ishydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety, and wherein R₅ represents a substitution located on anyposition of the ring, wherein R₅ is represented by the formula:

wherein R₆ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution ishydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety.
 5. The device of claim 4, wherein the two phthalimidegroups are in ortho position on the cyclohexane ring.
 6. The device ofclaim 1, wherein R is represented by the formula:

wherein R₇ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution ishydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety.
 7. The device of claim 1, wherein R is represented by theformula:

wherein R₉ represents one or more independently selected substitutionslocated on any position of the ring, wherein each substitution ishydrogen, an alkyl moiety containing up to fifteen carbon atoms, or anaryl moiety.
 8. The device of claim 1, wherein the phthalimide compoundis a bis-phthalimide.
 9. The device of claim 1, wherein the phthalimidecompound is selected from the group consisting of:


10. The device of claim 1, wherein the phthalimide compound is selectedfrom the group consisting of:


11. The device of claim 1, wherein the device is an organiclight-emitting device.
 12. The device of claim 11, wherein the organiclayer is an electron transport layer.
 13. The device of claim 1, whereinthe device is a solar cell.
 14. The device of claim 13, wherein theorganic layer is an exciton blocking layer.
 15. The device of claim 1,wherein the phthalimide compound has the formula:

wherein R_(A) represents one or more independently selectedsubstitutions located on any position of the ring, wherein eachsubstitution is a hydrogen, an alkyl moiety containing up to fifteencarbon atoms, or an aryl moiety, wherein R_(B) represents one or moreindependently selected substitutions located on any position of thering, wherein each substitution is a hydrogen, an alkyl moietycontaining up to fifteen carbon atoms, or an aryl moiety, and wherein Lis a 6-membered ring or a direct bond between the two phthalimidegroups.
 16. The device of claim 15, wherein L is a cyclohexane ringrepresented by the formula:

wherein R_(C) represents one or more independently selectedsubstitutions located on any position of the ring, wherein eachsubstitution is a hydrogen, an alkyl moiety containing up to fifteencarbon atoms, or an aryl moiety, and wherein the two phthalimide groupsare in ortho, meta, or para position on the cyclohexane ring.
 17. Thedevice of claim 15, wherein L is an phenyl ring represented by theformula:

wherein R_(D) represents one or more independently selectedsubstitutions located on any position of the ring, wherein eachsubstitution is a hydrogen, an alkyl moiety containing up to fifteencarbon atoms, or an aryl moiety, and wherein the two phthalimide groupsare in ortho, meta, or para position on the phenyl ring.
 18. The deviceof claim 17, wherein L is represented by the formula:

wherein the two phthalimide groups are in para position.
 19. The deviceof claim 18, wherein L is represented by the formula:


20. The device of claim 18, wherein L is represented by the formula:


21. The device of claim 16, wherein L is represented by the formula:

wherein the two phthalimide groups are in ortho position.
 22. The deviceof claim 21, wherein L is represented by the formula: